Uranyl Speciation on the Surface of Amidoximated Polyacrylonitrile Mats

SERS detection of uranyl based on MOF-coated gold nanooctahedron hybrid

The ability to sensitively and quantitatively detect uranyl in complex samples plays a vital role in environmental monitoring. In this work, an MOF-coated gold (Au) nanohybrid was synthesized for uranyl detection by surface-enhanced Raman scattering (SERS) technology. The MOF shell not only prevents the Au nanoparticles from rapid aggregation, but also effectively enhances the Raman signal of uranyl. A detection limit of as low as 0.5 μM could be achieved in solution, which could be comparable to the previously reported ones from SERS-based approaches. Moreover, the prepared SERS-active substrate was also applied to uranyl detection in real samples.

Heterometallic uranyl (hydroxyethyl)iminodiacetic acid (heidi) complexes: Molecular models for U(VI) uptake in complex media

Amidoximated absorbents (AO-PAN) effectively remove U(VI) from aqueous solution, but previous studies reported more variability for complex natural waters that contain additional confounding ions and molecules. Ternary phases containing U(VI), M(III) (M = Fe(III), Al(III), Ga(III)), and organic molecules exist under these conditions and cause heterogeneous U(VI) uptake on AO-PAN. The goal of the current study is to provide additional insights into the structural features ternary complexes using N-(2-hydroxyethyl)-iminodiacetic acid (HEIDI) as the model organic chelator and explore the relevance of these species on U(VI) capture. Three model compounds ([(UO2)(Fe)2(μ3-O)(C6NO5H8)2(H2O)4] (UFe2), ([(UO2)(Al)2(μ2-OH)(C6NO5H8)2(H2O)3] (UAl2) and [(UO2)(Ga)2(μ2-OH)(C6NO5H8)2(H2O)3] (UGa2)) were characterized by single-crystal X-ray diffraction. Raman spectra of the model compounds were compared with solution data and the ternary phases were noted in the case of Al(III) and Ga(III), but not in the Fe(III) system. U(VI) adsorption onto AO-PAN was not impacted by the presence of HEIDI or the trivalent metal species.

Recent advances and remaining barriers to the development of electrospun nanofiber and nanofiber composites for point-of-use and point-of-entry water treatment systems

In this review, we focus on electrospun nanofibers as a promising material alternative for the niche application of decentralized, point-of-use (POU) and point-of-entry (POE) water treatment systems. We focus our review on prior work with various formulations of electrospun materials, including nanofibers of carbon, pure metal oxides, functionalized polymers, and polymer-metal oxide composites, that exhibit analogous performance to media (e.g., activated carbon, ion exchange resins) commonly used in commercially available, certified POU/POE devices for contaminants including organic pollutants, metals (e.g., lead) and persistent oxyanions (e.g., nitrate). We then analyze the relevant strengths and remaining research and development opportunities of the relevant literature based on an evaluation framework that considers (i) performance comparison to commercial analogs; (ii) appropriate pollutant targets for POU/POE applications; (iii) testing in flow-through systems consistent with POU/POE applications; (iv) consideration of water quality effects; and (v) evaluation of material strength and longevity. We also identify several emerging issues in decentralized water treatment where nanofiber-based POU/POE devices could help meet existing needs including their use for treatment of uranium, disinfection, and in electrochemical treatment systems. To date, research has demonstrated promising material performance toward relevant targets for POU/POE applications, using appropriate aquatic matrices and considering material stability. To fully realize their promise as an emerging treatment technology, our analysis of the available literature reveals the need for more work that benchmarks nanofiber performance against established commercial analogs, as well as fabrication and performance validation at scales and under conditions simulating POU/POE water treatment.

U(VI) binding onto electrospun polymers functionalized with phosphonate surfactants

We previously observed that phosphonate functionalized electrospun nanofibers can uptake U(VI), making them promising materials for sensing and water treatment applications. Here, we investigate the optimal fabrication of these materials and their mechanism of U(VI) binding under the influence of environmentally relevant ions (e.g., Ca²⁺ and CO 3 2 - ). We found that U(VI) uptake was greatest on polyacrylonitrile (PAN) functionalized with longer-chain phosphonate surfactants (e.g., hexa- and octadecyl phosphonate; HDPA and ODPA, respectively), which were better retained in the nanofiber after surface segregation. Subsequent uptake experiments to better understand specific solid-liquid interfacial interactions were carried out using 5 mg of HDPA-functionalized PAN mats with 10 μM U at pH 6.8 in four systems with different combinations of solutions containing 5 mM calcium (Ca²⁺) and 5 mM bicarbonate ( HCO 3 - ). U uptake was similar in control solutions containing no Ca²⁺ and HCO 3 - (resulting in 19 ± 3% U uptake), and in those containing only 5 mM Ca²⁺ (resulting in 20 ± 3% U uptake). A decrease in U uptake (10 ± 4% U uptake) was observed in experiments with HCO 3 - , indicating that UO₂-CO₃ complexes may increase uranium solubility. Results from shell-by-shell EXAFS fitting, aqueous extractions, and surface-enhanced Raman scattering (SERS) indicate that U is bound to phosphonate as a monodentate inner sphere surface complex to one of the hydroxyls in the phosphonate functional groups. New knowledge derived from this study on material fabrication and solid-liquid interfacial interactions will help to advance technologies for use in the in-situ detection and treatment of U in water.

Complexation of uranyl(vi) with succinimidedioxime in comparison with glutarimidedioxime

Glutarimidedioxime favors 1 : 2 neutral uranyl complex species, whereas succinimidedioxime tends to form a cross-linked 2 : 2 binuclear complex with uranyl ions.